Bone conduction receiver



`Ian. 11, 1944.v R W lCARUSL 2,339,148

- BONE CONDUCTION RECEIVER Filed Dec. 29, 1942 2 Sheets-Sheet 1 "Y- INVENTOR. sf 58 29 El 7. IK CMM BY f Fig 4 WM Jan. 1l, 1944. R, w. CARLISLE ,BONE CONDUCTION RECEIVER Filed Dec. 29, 1942 2 Sheets-Sheet 2 INVENTOR.

BY a

m N M n A Fig. /2

Patented Jan. 11, 1944 BONE CQNDUCTION RECEIVER vRichard W. Carlisle, Elmsford, N. Y., asslllliill to Sonotone Corporation, Elmsford,

poration o! New Yorkl Application December 29, 1942, Serial No. 470.483

3 Claims.

This invention relates to bone conduction hearing aids and more particularly to bone conduction receivers for such hearing aids of the type disclosed in the copending application Serial No. 361,140 of H. W. Koren, tiled October 14, 1940 and assigned to the assignee of the present application, and which are small and light enough for comfortable and inconspicuous wear in contact with'the hearing inducing bone of the head and are eilicient enough to impart intelligible hearing of speech and music by bone conduction.

Among the objects of the invention is an improved bone'conduction receiver of the foregoing type formed of a piezo-electric crystal element to one side of which is secured ,a mechanically strong contact wall member so as to constitute with the crystal element an elastically deform- Fig. l2 is a simpliiled electrical circuit diagram, similar to Fig. 6, representing an analog of the mechanical system formed by a bone receiver, such as shown in Figs. 7 to 9.

The bone conduction receivers of the invention are designed for operation as a part of a wearable hearing aid small enough for inconspicuous wear on the body of the user, of the general type able vibratory unit having at least two driving vibratory portions interconnected through elastic elements oi the crystal element and the wall member to an intermediate driven bone-coupling portion of the wall member, the other side of the crystal being enclosed by a -cover member which is so secured to the contact wall member as to form therewith a protective enclosure for the crystal element while forming a part of the driving mass structure oi the bone receiver.

The foregoing and other objects ofthe invention will be best understood fromthe following description of exemplifications thereof, reference being had to the accompanying drawings wherein Fig. 1 is a diagrammatic view of a wearable bone conduction hearing aid employing a bone conduction receiver of the invention;

Fig. 2 is a vertical cross-sectional view along line 2-2 of Fig. 3 of a bone conduction receiver exemplifying the invention;

Fig. 3 is a horizontal cross-sectional view of the receiver along line 3-3 of Fig. 2;

Fig. 4 is a cross-sectional view of a receiver along line 4 4 of Fig. 3.

Fig. 5 is an electrical circuit diagram representing an analog of the mechanical system formed by a bone receiver, such as shown in Figs. 1 to 4;

Fig. .6 is a simplified form ofthe diagram of Fig.5;

Fig. 7 is a view similar to Fig. 2 illustrating another form. of bone receiver of the invention;

Fig. 8 is a cross-sectional view along line 9 8 of Fig. 7;

Fig. 9` is a view along line -9-9 of Fig. 2;

Figs. .10 and 11 are perspective views ot junction elements of the device shown in Figs. 7 to 9; and

described in the copending application Serial No. 418,857, tiled November 12, 1941 as a continua' tion-in-part of the application Serial No. 294,649, tiled September 13, 1939, and assigned to the assignee oi the present application. The general arrangement of shown in Fig. 1. It comprises a ilat compact amplitler casing I 3 small enoughfor inconspicuous wear, for instance, in the vest pocket of the user, the casing I3 housing a diaphragm driven Rochelle salt crystal microphone and an electron tube amplifier which ampliiies the input of the microphone. The ampliiier impresses the amplified microphone input through thelleads of a receiver cord I4 on a bone conduction 'receiver I5 which is held by a head band Il, oi' spring steel,

for instance, against a hearing inducing bone of the-user, such as the mastoid bone' behind the ear. The ampliiier is energized by an energy supply unit, shown in the form of a ilat compact battery aggregate I7, which is connected to the ampliiler casing through a battery cord I8 and is designed for inconspicuous wear hidden under the clothing of the user.

The boneconduction'receiver II, exemplifying one form of the invention, is shown in Figs. 2 to 4. 1t consists essentially of a vibrating structure 2l formed of a plate-like piezo-electric crystal vibrating member or unit 2l, which is united. as by cementing. along a substantial portion of its length to a relatively thin, mechanically strong and shockprooi, and elastically compliant strip or plate-like wall member 22, an intermediate portion 2i of which is held pressed against a hearing inducing bone 23 of the user.

The piezo-electric crystal unit 2| is provided with -foil electrodes secured to its faces and may embody one of the several types of designs de- U. S. Patents 1,802,782, 1,803,274; 1,803,275 and 1,995,275. The crystal element 2|* shown is a bimorph which may be designed in the well-known mannerto operate as a bender. When alternating -voltage is applied to the electrodes of such crystal unit, it will flex at the center during each alternation. The resilient bonecontacting strip or wall 22 is combined with the piezo-electric unit 2l to form therewith a unitary such wearable hearing aid mechanically strong and shockproof vibrating ture 2l so formed is so arranged that when its 8 bone-contacting portion 2| is held against the jbones, the masses of its resiliently carried vibratory end portions u, :s form, with the mass of Y the bones, a vibratory system which operates so that the vibrations of said masses relatively to A the bone-contacting portion 2l, exert thereon inertia reaction'forces acting in a general direction toward the bone-contacting surface and imparting therethrough to the bones vibrations of large intensity and small amplitude required for inducing intelligible hearing of speech by bone conduction. Two leads in the form of fiat metal foil strips 21 extending from the electrode sur' faces of the crystal unit 2| impress' thereon the speech frequency voltage oscillations which ixn- 2o part to the vibratory structure 2 0 the desired vibratory motion.

.' In the form shown, the piezo-electric crystal unit 2| is of a fiat double-trapezoidal shape,.and

only its center and its relatively narrow end por- 25 tions are united across thinspacerK-like junction elements 2l. 22 to the compliant contact plate 22. 'l'he thin spacer elements 2l. 2l are united to v the facing surfaces of the crystal unit 2| and the contact plate 22 by a strong lcementitious kmate- 30 rial, such as Vulcalock or nitrocellulose cement. The junction elements 28, 29 may be made from a material, such as Viscoloid, which will flow and yield enough to prevent the exertion of abnormally large forces on the crystal unit 2| in its 35 lengthwise direction during the vibrations of the vibrating structure 20,` while providing a very good and still.' coupling junction between the crystal unit and the resilient contact plate 22 in the transverse direction so that the resulting 40 vibrating structure 20 shall vibrate in the desired manner described above. In particular, the Junction pads 2l connecting the end portions of the flexible crystal unit 20 'to thek flexible contact plate 22 are stil! enough to assure'` a very stiff cou- 45 'filing between them in the' directions of their vibratory pending motion. In some cases the spacer elements 28. ,28 may be made of .a grade of neoprene which has properties similar to those of Viscoloid, but is stiffer, Viscoloid being used for 5 protected against damage.

the central Junction elements 29, while the end spacer elements 28 are made of the stiifer neoprene.

The bone contacting strip or wall 22 is preferably made of a sheet metal element 3| to 55 which may be united an outer layer 22 of s, suitable synthetic resin material, a'thin coating of which may also be united to its inner surface facing the crystal unit. Alternatively, the resilient contact strip 22 may be made of a lamina- 60 tion formed of several layers `of thin fabric or paper impregnated and united by a cementitious synthetic resin, such as a phenolic condensation product orsome other integration-resistant resin. v

The sheet metal element 3| of the contact plate 22 is provided'with small perforations occupying a 'sufiicient area and being so arranged as to keep the stiffness of the contact plate 22 sufilciently low and give it the required degree oi resiliency. The perforations serve also as interlocking junctions with the synthetic resin material united to the surfaces of the metal sheet 13|, so as to permit the construction of the con- 2 assauts the contact plate 22 may be madefiofa thin lamination of thin fibrous sheets bonded with a synthetic resin.

In. designing avibrating structure 20 for an inertia reaction bone conduction receiver of the type described above, it is important to assure that when the proper portion of it is held coupled to the bones, the relatively small mass of its resiliently carried vibratory portion forms with the compliance of the head and the mass of the bones a vibratingsystem which vibrates efflciently over the principal part of the speech frequency range when actuated by the output voltage of a hearing aid amplifier unit of the type referred to hereinabove.

To this end, the vibrating structure has to be designed so`v that when its contact portion is held coupled to the head, the relatively small mass of its -resiliently carried vibratory portions resonates broadly with .the compliance of the elastic portionsf'of the crystal unit 20 and of the contact plate 22,'\so that it forms with the compliance of the flesh and the relatively much larger mass of the bones of the head a vibrating system which has aresonant frequency in the principal part of the speech frequency range so that when it is actuated vby speech frequency oscillations, it will give a good response'over the speech lfrequency range, and it will impart to the'bones inertia reaction forces sumcient tofinduce intelligible hearing of speech by bone conduction.L

One end of the contact plate 2211s provided with a terminal block projection 4| in which, are y insulatingly mounted two terminal bushings' ,4,2 which are engaged by the plugs of the re er cord I5 through which the electric speech frelquency oscillations are impressed on the crystal element 2| of the receiver. The bushings may be of the type described in the copending application Serial No. 346,112, filed July 18, 1940 and their inner ends are connected to two tin foil lead strips 21 extending from the electrodes ofthe piezo-electric element. The tin foil lead strips 21,are shown folded flat along the surfaces of thecrystal element 2| and, along the underly-y ing surface portions ofthe contact plate 22 leading to the terminal block, suitable insulating sheet elements', for instance, of cellulose acetate being placed above', and if required below, the tin foil strips so as to keep them insulated and In order to protect the crystal element 2| against excessive humidity, a shell M of very thin moisture impervious foil, of aluminum, for instance, shaped to conform to the outline of the crystal element 2|, is placed thereover, thestance, such as leather, are shown placed inside the crystal enclosure formed by theshell 44 in order to assure that the crystal does not become excessively dry and that the humidityy con' l ditions in the enclosureA are' conducive to the elcient operation of thev crystal.-

According to the present invention, a rigid cover member 55 serving to enclose and protect tact plate by a molding process. Alternatively, 75 the outer side of the crystal element 2| is so connected to the vibratory portions of the contact wall member 22 extending on both sides of its bone-coupling portion as to form with these vibratory contact wall portions and the crystal portions united thereto the driving vibratory mass structure proportioned to assure that the vibratory system which it forms with the large mass of the bones operates with the desired resonant frequency.

In the form shown, the cover 55 forins a rlsid structure having on three sides the side walls 55 enclosing the space in which the crystal is confined. The free edge portion of the upper cover wall 55 is held clamped to the upwardly facing surface of the terminal block Il, as by a screw 51, threadedly engaging an internally threaded bushing 58 embedded in the terminal block.

The upper surface of the terminal block 4| is suiiiciently curved and the surface of the hole 1 in the cover plate 55 which is engaged by-the head of the clamping screw 51 is so shaped as to permit limited tilting movement of the cover relatively to the terminal block ll. The other end of the cover is shown held clamped, as by screws 6|, to the reinforced upper ends of upwardly projecting links 52 extending from the contact wall 22, the links being so shaped and arranged as to oiier substantially negligible or zero resistance to forces exerted thereon in a direction parallel to the' longer axis of the vibrating structure 20 and its crystal element, while providing a. good coupling connection and substantially rigid junctions for forces transmitted in the direction of the links 62 between the contact plate 22 and the facing portion of the cover 55.

In other words, the cover 55 is-` so joined to the vibrating structure 20 formed by the crystal element 2l and the resilient contact plate 22 united thereto as to offer substantially zero resistance to small elongations and contractions of the vibrating structure 20 and its contact plate 22 in the direction of their length, while assuring that the mass of the cover 55 vibrates substantially in unison with the end portions of the vibrating structure 20 and its contact plate 22 in a direction generally perpendicular to the bone-contacting surface portion of the contact plate 22.

By this arrangement, the cover plate 55, which serves tol protect the crystal unit against external mechanical forces, is also utilized to serve as the additional mass required in order to give the vibrating structure 20 the desired resonant frequency characteristics in the principal part of the speech frequency range. vThe cover is designed with suiiicient mass, as-by making it partially or entirely of heavy metal, so that its mass is eiective in giving to the vibrating unit 20 the required resonance characteristics.

The links 52 which serve as a junction between the contact plate 22 and the overlying portion of the cover 55 may bel formed as separate units, the lower bent portions of which are united, as by riveting or spot welding. to the contact plate 22. In the form shown, the links 62 are formed by cutting out and bending outward a strip portion of the metallic sheet element 3l forming one layer of lthe resilient contact plate 22.

Means are also provided for maintaining a good contact coupling connection between the nodal bone-contacting portion 26 of the vibrating structure 20 and the bone 23 against which it is held pressed, as by a head band l5. The head band may be of the type described in U. S.

tact wall member 22. The central pivot hole projections 51 of the'contact member are shown made by the molded material of the contact plate having embedded therein upward extensions of the sheet metal element 3| of the contact wall.

A bone receiver of the type described above will operate generally as follows: When speech frequency alternating voltages are applied toy the electrodes of the crystal element, the two ends of the crystal elements flex relatively to the center so that the two crystal ends together with the adjacent facing portions of the flexible contact plate, as well as the mass of the cover wall connected thereto, vibrate relatively to the central portion of the crystal element and the central portion of the contact plate which are held coupled to the bone. In such bone receiver, the vibrating masses of the end portions of the crystal 'element and the contact plate, as well as the mass of the cover wall connected thereto, are thus subjected to acceleration, and as a result exert on the central head coupling portion ofthe contact plate and therethrough on the bones the inertia reaction forces required to induce hearing by bone conduction.

When a bone receiver, such as described above in connection with Figs. 2 to 4, is held coupled to the hearing inducing bones of a user, it forms a vibrating system, the elements of which may be represented by the analogous electric circuit of Fig. 5. In the diagram Fig. 5:

E represents the source of electrical energy oscillations impressed upon the receiver electrodes;

InductancevM-l represents the vibrating mass of the casing cover and the other portions of the receiver structure which vibrate relatively to its bone coupling portion;

Inductance M-Z represents the vibrating mass of the crystal element;

Inductance M-S'represents the vibrating mass of the bone contacting portion 2 6 of the contact wall 22; 4

Inductance M-l represents the mass of the bones and the head;

Capacity C-I represents the compliance of the crystal element;

Capacity C-2 represents the compliance of the exible contact wall 22;

Capacity 0 3 represents the compliance of the stii junctions 28, 29 between the crystal element and the flexible contact plate 22;

Capacity C-4 represents the compliance of the esh against which the contacting portion of the bone receiver is held pressed; and

Resistances R-I and Rf-2 represent the effective resistance of the flesh and the bones of the head in which the supplied energy is dissipated.

Since the stiifness of the junction elements represented by C-3 is relatively large, and the masses M-2 and M-3 ofthe crystal element and the contact element are relatively small, compared to the mass of the cover wall 55, the diagram of Fig. 5 may be replaced by the simpliiied diagram of Fig. 6. At Athe resonant frequency of such system, the velocity of the vibrations produced by the vibrating energy E impressed upon the receiver will be a maximum and will be represpented in Fig. 6 by the current I-l. At such 4 resonant frequency, this maximum velocity, corresponding to the current'I-I, impresses a maximum force across the load comprisedof the ilesh compliance C-4, imparting thereto a velocity represented by the current I-2 in Fig. 6. At

frequencies higher than resonance, the current I-l diminishes, but the current I-2 continues without vsubstantial diminution, and there is, therefore, no deilnite cut-oli for higher frequencies.

Crystal transducer elements, such as used in thebone receiver of the invention, are very enlcient for high frequencies. Inaddition, the small vacuum tubes used in the hearing aid amplifiers become frequently overloaded, and under such conditions they are a source of disturbing high frequency oscillations. It is accordingly important to assure that in a hearing aid bone receiver, undesirable frequencies which are not important for intelligible speech, such as above 4000 cycles, should not be transmitted to the bones. Ac'- cording to one phase of the invention, a bone receiver of the foregoing type is so designed as to embody a lter which prevents the transmission of undesirable disturbing high frequencies to the bones of the head. i

Figs. 7 to 12 illustrate one form of such bone receiver of the invention embodying in its strucl high frequencies to the hearing inducing bones As shown in Figs. 'l and 8, the bone receiver has a vibratory crystal element 20, a compliant contact-plate wall member 22a and a cover wall member joined into a case-like vibratory unit generally similar to that of Figs. 2 to `4, so that the middle of the crystal element 20 and the contact -plate 22a vibrate as a unit when the intermediate bone-coupling portion 2 6 of the contact plate 22a is held coupled to the bones, the mass of the cover wall 55 being interconnected with the vibrating end portions of the contact plate 22a and constituting with their masses the driving mass body of the vibrating unit.

In the bone receiver of Figs. '7 and 8, the stiff interconnection between the lengthwise ends .of the crystal'element 20 and the facing portions of the contact plate 22a are formed by relatively stiff junction members 1|, of a metal strip, for instance, as shown in detail in Fig. 10. Each junction member 1l has at one end two clamping arms 12, secured. as by cementing, to the crystal portion, and another arm 13, secured, as

` by cementing, to the facing portion of the contact plate 22a. The intermediate junction portion of strip 1l extending between the crystal element 20 and the contact plate is proportioned to secure a very stiff coupling between them while yielding to forces exerted between them `in the longitudinal direction of the crystal element. Such junction member 1| may be made either of a single metal strip as shown in Fig. 1l, or of two metal strips, in the way shown in Fig; 10.

The central part of the crystal element 20 has its two sidev portions clamped to the facing portions of the contact wall by 'two junction members 15. Each junctionimember 15 hasat one end an arm 16 secured. as by cementing, to

the underlying portion of the vcontact plate 22a.

The projecting portion of4 each Vjunction membei` 15 is bent to form at its other end two arms 11 secured, as by cementing, to the side portions of the central part of the crystal elementand an of the user. the bone coupling portion 26 of the contact plate 22a is provided with a relatively large mass 26a.

It will be apparent to those skilled in the art that the novel principles of thevinvention dis- A closed herein in connection with specic yexemplifications thereof' will suggestyarios other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the'specifc exemplifications of the invention described herein.

Iclaim:

1. In a wearable bone conduction hearing aid device` a bone-receiver vibratory unit designed to be worn coupled to the massive bone body surrounding the inner ears of the user; said vibratory unit comprising a'piezohel'ectric crystal element,

and two mechanically-strong wall members extending adjacent to the opposite sides of said crystal element; one of said wall members constituting4l a contact member and having at least two spaced portions united to two facing spaced portions of said crystal element; said crystal element and said contact member having intermediate elastic elements and being joined into an elastically deformable vibratory structure having at least two driving vibratory portions interconnected through said elastic elements to an intermediate driven bone-coupling portion thereof; the

of said contact member constitute the vibratory- `mass of driving portions of said vibratory unit;

said driving portions being formed of portions of said crystal element and portions of said two wall members and having a substantial, but relativelysmall vibratory mass which is onlya small fraction of the mass of said body; electrode means associated with said crystal element for producing vibrations of said driving portions relatively to said intermediate bone-coupling portion; a wall portion of said intermediate bone-coupling portion having an outward contact surface arranged to be held coupled against said body so as to resiliently carry saiddriving portions in a vibratory condition and to operatively couple through said elastic elements the small mass of said driving-portions with said body into a vibra.- tory system having a resonant frequency which gives a good vibratory response in the speech frequency range.

. 2. In a wearablebone conduction hearing ald device, a bone-receiver vibratory unit designed to be worn coupled 4to the massive bone body surrounding the inner ears of the user; saidvvlbratory unit comprising a piezo-electric crystal element, and two mechanically-strong wall members extending adjacent to the opposite sides of said crystal element; one of said wall members constituting a contact member and having at least two spaced portions united to two facingv spaced portions of said crystal element; said crystal element and said contact member having intermediate elastic elements and being joined into an elastically deformable vibratory structure having at least two driving vibratory portions interconnected through, said elastic elements to an intermediate driven bone-coupling portion thereof the other of said Wall members constituting a cover member protectingly enclosing said crystal element and being secured only to said two spacedv portions of said contact member so that a substantial mass part of said cover member and the masses of said two spaced portions of said crys tal element and of said two`spaced portions of said, contact member constitute the vibratory mass of driving portionsof said vibratory unit; said driving portions being formed o f portions of said crystal element and portions of said two wall y members and having'a vibratory mass between about two to about forty grams which is only a small fraction of the mass of said body; electrode means associated with said crystal element for producing vibrations of said driving portions relatively to said intermediate bone-coupling portion and causing said bone-coupling portion to 'operate as a nodal portion of said vibratoryvunit;

a wall portion of said intermediate bone-coupling rounding the inner ears of the user.; said vibrav tory unit comprising a. piezo-electric crystal element, and two mechanically-strong wall members extending adjacent to the opposite sides of said crystal element; one of said wall members constituting a contact member and having at.' least two spaced portions united to two facing spaced portions of said crystal element; said crystal element and said contact member having intermediate elastic elements and being joined into 'an elastically deformable vibratory structure having at least two driving vibratory portions interconnected through said elastic elements to an intermediate driven bone-coupling portion thereof; the'other of said wall members constituting a cover member protectingly enclosing said crystal element and being secured only to said two spaced portions of said contact. member so that a substantial mass part of said cover member and the masses of said'two spaced portions of said crystal element and of said two spaced portions of said fcontact member constitute the vibratory mass of and having a vibratory mass between about two to portion having an outward contact surface arv tory system having a resonant frequency which l gives a good vibratory response in the speech fre.- quency range; said contact surface being arranged to form part of an exposed Wall surface of said vibratory unit suiilciently extended and so arranged under and relatively to the mass of said driving portions asto maintain said vibratory unit in a stable-equilibrium coupling position on the bone under a relatively small external cou pling force for eiiciently transmitting to the bone the vibratory forces exerted by said unit.

3. In a Wearable bone conduction hearing aid device, a bone-receiver lvibratory unit designed to be worn coupled to the massive bone body surintermediate bone-coupling portion and causing said bone-coupling portion to operatel as a nodal portion of said vibratory unit; a wall portion of said intermediate bone-coupling portion having anoutward contact surface arranged to be held coupled against said body so as to resiliently carry said driving portions in a vibratory condition and to operatively couple throughv said elastic elements the small mass of said driving portions with said body into a vibratory system having a resonant frequency which gives a good vibratory response in the speech frequency range; and ex- 

